In general, liquid crystal display devices comprising a pair of substrates and a liquid crystal layer held between these substrates are known. In the liquid crystal display device, liquid crystal molecules of the liquid crystal display layer are driven by an electric field produced between pixel electrodes provided in respective pixels and a common electrode provided over a plurality of pixels, to thereby display an image.
It has been found by a reliability test, etc. that water easily enters an edge portion of a display area in a liquid crystal display device. If water enters it, there is a case where ionic impurities seep into a liquid crystal layer, thus lowering a drive voltage to the liquid crystal layer. If the drive voltage lowers, the brightness of an image displayed in a display area can become non-uniform. Furthermore, in a control method in which a AC drive voltage is applied to a liquid crystal layer, a so-called flicker can occur in which the brightness of a displayed image periodically vary in accordance with the polarity of the above ionic impurities. This flicker is remarkably visibly recognized in the case of decreasing the frequency of the drive voltage for the purpose of reducing power consumption or the like.